Speaker
Description
Heavy quarks (charm and beauty) are mainly produced in hard-scattering processes among partons in ultrarelativistic hadronic collisions at the LHC. In heavy-ion collisions, where a quark-gluon plasma (QGP) state is produced, charm and beauty quarks are produced on a timescale shorter than the medium formation time, being sensitive to the initial angular momentum of the fireball and to the magnetic field produced perpendicularly to the reaction plane in non-central heavy-ion collisions. In the presence of a large angular momentum and initial magnetic field, the charm quark can be polarised, and the quark polarisation is expected to be transferred to the hadron during the hadronization process. Experimentally, heavy-flavour polarisation can be probed by measuring either the spin density matrix element $\rho_{00}$ of spin-1 bosons (as the D$^{*+}$ meson) or the longitudinal polarization $P_{\rm z}$ of spin ½ fermions (as the $\Lambda_{\rm c}^{+}$ baryon). Measurements in pp collisions provide a crucial baseline to disentangle the amount of charm-hadron polarization induced by the charm-quark polarization inherited from the initial stage of heavy-ion collisions.
In this contribution, the first measurement of the $\rho_{00}$ parameter of D$^{*+}$ meson in Pb-Pb collisions at $\sqrt{s_\mathrm{NN}}=5.02~$TeV, exploiting the data sample collected by the ALICE Collaboration during the LHC Run 2, is shown. Moreover, the $\rho_{00}$ parameter of D$^{*+}$ mesons and the longitudinal polarization $P_{\rm z}$ of $\Lambda_{\rm c}^{+}$ baryon measured in pp collisions at $\sqrt{s}=13.6~$TeV collected during the LHC Run 3 are presented. In this case, the measurements are performed also for charm hadrons originating from b-hadron decays, for which the helicity conservation in weak decays should imply a non-zero polarization of the produced charm hadrons.
| Category | Experiment |
|---|---|
| Collaboration (if applicable) | ALICE |
